a. Field of the Invention
The instant invention relates to digital power factor control of analog current (AC) to direct current (DC) converters.
b. Background
Power factor correction (PFC) boost rectifiers are used in a wide range of applications to limit harmonic current emissions, such as those that are required to meet the IEC EN61000-3-2 standard. At low-to-medium power levels, a transition-mode control (i.e. critical conduction mode, or operation at the boundary of continuous conduction mode (CCM) and discontinuous conduction mode (DCM)), which offers simplicity and performance advantages, is widely used and supported by a range of commercially available low-cost controllers. At higher power levels (typically above several hundred Watts), CCM operation is often preferred because of lower conduction losses and reduced EMI filtering requirements. Averaged current mode control in combination with a slow voltage control loop and a multiplier, which is a well-known control approach for CCM PFC, requires a more complex implementation compared to the transition-mode control. With the motivation of simplicity comparable to transition-mode or DCM operation, together with low-harmonic, low conduction loss, and low EMI performance in CCM, the nonlinear-carrier (NLC) control technique was introduced in Maksimovic et al., Nonlinear-Carrier Control for High-Power-Factor Boost Rectifiers, Power Electronics, IEEE Transactions on, Volume 11, Issue 4, July 1996, pp. 578-84 and in U.S. Pat. No. 5,867,379 entitled “Non-Linear Carrier Controllers for High Power Factor Rectification,” filed by Dragan Maksimovic et al., and issued on Feb. 2, 1999. This technique eliminated the needs for input voltage sensing, current loop compensation, and a precision analog multiplier. Variations of the analog NLC control approach have also been reported and used in commercially available controllers. Digital PFC controllers, offering improved system interface, power management features, support for multi-module operation, and improved voltage-loop dynamic responses, have recently received increased attention. However, most of the digital PFC control techniques reported so far have been based on DSP or microcontroller implementations, or have relied on multiple current samples per switching period.